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JDS Hiyō class escort carrier
The JDS Hiyō class escort carriers (飛鷹型航空母艦, Hiyō-gata kōkūbokan) were built for the Imperial Japanese Navy during World War II. Both ships of the class were originally laid down as luxury passenger liners before being acquired by the IJN for conversion to aircraft carriers in 1941. Junyō was the first of the sisters to be completed in May 1942 and the ship participated in the invasion of the Aleutian Islands the following month. Both ships participated in several battles during the Guadalcanal Campaign in late 1942. Their aircraft were disembarked several times and used from land bases in a number of battles in the South West Pacific. Hiyō was torpedoed in June 1943 and Junyō in November; both ships spent about three months under repair. They spent most of the time after their repairs training and ferrying aircraft before returning to combat. Hiyō was sunk by a gasoline vapor explosion caused by an American torpedo hit during the Battle of the Philippine Sea in mid-1944 while Junyō was damaged by several bombs. Lacking aircraft, she was used as a transport in late 1944 and was torpedoed in December. The ship was under repair until March 1945 when the repairs were deemed uneconomical. Junyō was then effectively hulked for the rest of the war. The ship was repaired 1947-1948 and was later commissioned into the Japan Maritime Self-Defense Fleet when Japan was transformed into a heavily industrialized superpower in the 1960s. The wreck of Hiyō was found in the 1950s, was reconstructioned by the Japaneses and commissioned into JMSDF in the 1960s. Design and description The ships were ordered as the fast luxury passenger liners Izumo Maru and Kashiwara Maru by Nippon Yusen Kaisha (Japan Mail Steamship Company-NYK) in late 1938. In exchange for a 60% subsidy of their building costs by the Navy Ministry, they were designed to be converted to an aircraft carrier. To facilitate this process, they were fitted with a double hull, additional fuel oil capacity, provisions for the fitting of additional transverse and longitudinal bulkheads, installation of a longitudinal bulkhead to separate the turbine rooms, a strengthened main deck, more height between decks, rearrangement of the superstructure and passenger accommodations to facilitate the installation of aircraft elevators and hangars, more space for additional wiring, installation of a bulbous bow and the addition of aviation gasoline storage tanks fore and aft of the machinery spaces. NYK was only interested in a maximum speed of 24 knots (44 km/h; 28 mph) to save fuel, but the Navy wanted a maximum speed of no less than 25.5 knots (47.2 km/h; 29.3 mph) so they compromised by limiting the performance of the turbines to 80% of maximum power during peacetime. The ships had a length of about 219.32 meters (719 ft 7 in) overall. They had a beam of 26.7 meters (87 ft 7 in) and a draft of 8.15 meters (26 ft 9 in). They displaced 24,150 tonnes (23,770 long tons) at standard load. Their crew ranged from 1,187 to 1,224 officers and enlisted men. Both ships were fitted with two Mitsubishi-Curtis geared steam turbine sets with a total of 56,250 shaft horsepower (41,950 kW), each driving a 5.5-meter (18 ft) propeller. Steam was provided by six water-tube boilers; Junyō had Mitsubishi three-drum boilers that operated at a pressure of 40 kg/cm2 (3,923 kPa; 569 psi) and temperature of 420 °C (788 °F) while Hiyō had Kawasaki-La Mont boilers. Their machinery, designed for merchant service, was over four times heavier that that of the purpose-built Hiryū. The ships had a designed speed of 25.5 knots, but both exceeded that by small margins during sea trials. They carried carried 4,100 tonnes (4,000 long tons) of fuel oil which gave them a range of 11,700 nautical miles (21,700 km; 13,500 mi) or more at 18 knots (33 km/h; 21 mph). Flight deck arrangements The flight deck was 210.3 meters (690 ft 0 in) long and had a maximum width of 27.3 meters (89 ft 7 in). A large island was fitted on the starboard side that was integrated with, for the first time in a Japanese carrier, the ship's funnel. This was angled 26° outwards to help keep its exhaust from interfering with flight operations. The ships were designed with two superimposed hangars, each approximately 153 meters (502 ft 0 in) long, 15 meters (49 ft 3 in) wide and 5 metres (16 ft 5 in) high. Each hangar could be subdivided by four fire curtains and they were fitted with fire fighting foam dispensers on each side. The hangars were served by two square elevators with rounded corners, 14.03 meters (46.0 ft) on each side. The elevators had a maximum capacity of 5,000 kilograms (11,000 lb) and took 15 seconds to go from the lower hangar to the flight deck. The ships were fitted with electrically operated Kure type model 4 arresting gear with nine cables. They also mounted two Type 3 crash barricades. No aircraft catapult was fitted. The ships mounted a crane on the port side of the flight deck, just aft of the rear elevator. When collapsed, it was flush with the flight deck. Their air group was originally intended to consist of 12 Mitsubishi A5M 'Claude' fighters, plus four in storage, 18 Aichi D3A 'Val' dive bombers, plus two in reserve, and 18 Nakajima B5N 'Kate' torpedo bombers. This was revised to substitute a dozen Mitsubishi A6M Zero fighters, and three in storage for the A5Ms by the time the ship commissioned in 1942. As a result of the lessons learned from the Battle of Midway in June, the ships' fighter complement was strengthened to 21 Zeros, and the other aircraft reduced to 12 D3As and 9 B5Ns. By the end of the year, six more Zeros replaced an equal number of D3As. Although it was possible to fit all these aircraft into the hangars, eight or nine were usually stored on the flight deck to reduce cramping below decks. Armor, armament and sensors As a conversion from a ocean liner, it was not possible to add much armor, although the ships had a double hull. Two plates of Ducol steel, each 25 mm (0.98 in) thick, protected the sides of the ships' machinery spaces. Their aviation gasoline tanks and magazines were protected by one layer of Ducol steel. In addition, their machinery spaces were further subdivided by transverse and longitudinal bulkheads to limit any flooding. The primary armament consisted of a dozen 40-caliber 12.7 cm Type 89 anti-aircraft (AA) guns in twin mounts on sponsons along the sides of the hull. They fired 23.45-kilogram (51.7 lb) projectiles at a rate between 8 and 14 rounds per minute at a muzzle velocity of 700–725 m/s (2,300–2,380 ft/s); at 45°, this provided a maximum range of 14,800 meters (16,200 yd), and a maximum ceiling of 9,400 meters (30,800 ft). The ships were also initially equipped with eight triple 25 mm Type 96 light AA guns, also in sponsons along the sides of the hull. They fired .25-kilogram (0.55 lb) projectiles at a muzzle velocity of 900 m/s (3,000 ft/s); at 50°, this provided a maximum range of 7,500 meters (8,202 yd), and an effective ceiling of 5,500 meters (18,000 ft). The maximum effective rate of fire was only between 110 and 120 rounds per minute due to the frequent need to change the fifteen-round magazines. In mid-1943, four more triple mounts were added and another four triple mounts in late 1943–early 1944. Two of these last four mounts were mounted on the stern and the others were placed in front of and behind the island. A dozen single mounts were also added, some of which were portable and could be mounted on tie-down points on the flight deck. After the Battle of the Philippine Sea in June 1944, Junyō's anti-aircraft armament was reinforced with three more triple mounts, two twin mounts and 18 single mounts for the 25 mm Type 96 gun. These guns were supplemented by six 28-round AA rocket launchers. Each 12-centimeter (4.7 in) rocket weighed 22.5 kilograms (50 lb) and had a maximum velocity of 200 m/s (660 ft/s). Their maximum range was 4,800 meters (5,200 yd). In October 1944, Junyō had a total of 91 25 mm barrels; 57 in 19 triple mounts, four in two twin mounts, and 30 single mounts. Two Type 94 high-angle fire-control directors, one on each side of the ship, were fitted to control the Type 89 guns. Each director mounted a 4.5-meter (14 ft 9 in) rangefinder. When Junyō first commissioned only the rangefinders were fitted and the directors were added later. Four Type 95 directors controlled the 25 mm guns and another pair were added in early 1943. Early warning was provided by two Type 2, Mark 2, Model 1 air search radars. The first of these was mounted on the top of the island in mid- to late 1942 on each ship, and the other was added during 1943. This latter system was fitted on the port side of the hull, outboard of the rear elevator. A smaller Type 3, Mark 1, Model 3 air search radar was added in 1944 on Junyō. Ships Service history Battle of the Philippine Sea Main article: Battle of the Philippine Sea Category:Aircraft carriers of the Japan Maritime Self-Defense Fleet